The objective of this project is to measure variation in bioaccumulation and biomagnification of potentially toxic metals in lakes throughout the Northeastern region of the U.S.A., with the end goals of understanding effects of hazardous substances on ecological systems, and the influence of food web structure on bioavailability to humans. Metals believed to vary with respect to their potential for bioaccumulation in natural systems will be compared (cadmium, mercury, arsenic and lead). The project addresses several general questions with a combination of field collections and laboratory experiments; (i) To what extent is the variation in biomagnification of metals in freshwater systems dependent on the food web structure, degree of human impact, or lake thermal mixing regime? (ii) To what extent is variation in the bioaccumulation of metals in freshwater organisms dependent on the metal type, food web group or other physical or chemical factors? (iii) How do demographic responses of different food web groups to toxic metals relate to their body burden of accumulated metals and their biochemical responses to metal toxicity. Can these biochemical responses be used to detect metal stress in the field? This proposal has three specific aims that relate to these questions. The first is to provide an estimate of variation in the metal levels in fresh water food webs, representative of lake types in the Northeast of the U.S.A. An extensive field survey of 50 lakes selected from more than 1,000 lakes in the Northeastern U.S.A. will be conducted. Lakes will be selected from a survey being conducted by the USEPA (EMAP-SW) to evaluate the current status of US environmental resources (Stemberger, PI). Data on food web structure, pH and thermal ratification patterns (but not metal concentrations) are already available for these lakes. Measurements of metal concentration (lead, arsenic, cadmium, and total mercury) in the water and in the tissue of different members of the planktonic pelagic food web will be analysed in each lake, together with other parameters known to correlate to ecosystem health. The second aim is to investigate rates of metal bioaccumulation and the potential for biomagnification at the level of species and functional group. This requires an intensive sampling program, during which a subset of the lakes (10-20) will be sampled in greater detail. This subset will be chosen to maximize comparisons of lakes that vary with proximity to urban centers, superfund sites, food web structure, metal levels, and temperature regime. On two dates in the growing season, levels of metals will be assessed in specific zooplankton taxa, in different age classes within these taxa, and in the tissues of planktivorous and piscivorous fish. In this survey, methyl-Hg will also be measured. The third aim is to investigate mechanisms underlying differences in metal accumulation and magnification operating within these taxa over their life cycle and in aquatic food webs dominated by different species. The focus is on establishing the relationship between body burden, biochemical assays of toxic stress, population viability, and community food web structure. This will be accomplished with experimental studies of variation in the metal body burden associated with differences in the age, size and species identity of zooplankton, under controlled conditions in the laboratory. Relations between biochemical indicators of metal stress in zooplankton and their demographic consequences, will be used to explore their potential use as a field indicator of ecosystem stress. Relevance of Project to RFA: Studies of specific toxic agents, such as metals, and simple and complex mixtures. Studies on the effect of hazardous substances on ecological systems, designed to study the resistance and resilience to the impact of tonics and leachates on ecosystems. Studies on the effect of hazardous substances on cellular and .... processes.